Chousin - trio who created the universe
Lord of nightmare
Locke - immortal and nearly omnipotent
Demonbane - Demonbane is a mech which
- has infinite speed, power, and everything else
- can destroy multiverses
- time-space control
- if it dies, it goes back 5 sec.
- can survive from not existing. so, it can't be removed from existence

Tenchi Masaki - omnipotent. Even if you argue that he isn't, he fought in space without oxygen (I believe) and escaped black hole and traveled far faster than light.

The people I mentioned are far far far stronger than Goku and Alucard. Not even death note can kill some of them.

As far as what the intention of the question being pure character battle potential, I would have to say Hibari Kyoya is the most overpowering character to other characters within his own universe. I've never seen a character pull off as many one sided battles as he has.

As far as the actual strongest I would either have to agree with the person who said Haruhi Suzumiya above or Inoue from Bleach. Haruhi is literally a being akin to God that unconciously shapes the universe to her whim. (Of course I would assume if she was aware of her powers she would be capable of doing it conciously as well). Inoue is in a similar boat on a not so grand scale with her ability not actually being healing but being able to deny the reality of anything within her ability's field.

I don't know...I mean Kaworu Nagisa from Evangelion is his own Mom technically...that's pretty powerful to me, lol.
Lol or when Taro from MM! goes all Super Saiyan from all the Hentai Power he gathered from everyone in the world was pretty freaking powerful